GB2043996A

GB2043996A - Thickness shear quartz crystal oscillator

Info

Publication number: GB2043996A
Application number: GB7943677A
Authority: GB
Original assignee: Nihon Dempa Kogyo Co Ltd
Current assignee: Nihon Dempa Kogyo Co Ltd
Priority date: 1978-12-27
Filing date: 1979-12-19
Publication date: 1980-10-08
Also published as: CH627913GA3; DE2951815C2; CH627913B; US4476411A; DE2951815A1; GB2043996B

Abstract

A thickness shear quartz crystal oscillator has two major surfaces which extend in the direction the of X axis of the crystal and which are 5mm to 10mm long. X-Z plane defined by the X axis and Z axis of the crystal is rotated about the X axis by 35 DEG 08' to 35 DEG 16' so that the major surfaces are parallel to an X-Z' plane defined by the X axis and an imaginary Z' axis inclined to the Z axis at 35 DEG 08' to 35 DEG 16'. One of the major surfaces is displaced in the direction of the Z' axis to thereby cause the side faces of the oscillator to incline at an angle of 4 DEG to 6 DEG .

Description

1 GB 2 043 996 A 1

SPECIFICATION Thickness shear quartz crystal oscillator

This invention relates to a thickness shear quartz crystal oscillator which can be made small and light and which has excellent electric 70 characteristics.

Generally, an AT-cut thickness shear quartz crystal oscillator exhibits a frequency-temperature characteristic which is represented by a three dimensional curve and is stable against temperature variation. Thus, it is used as a reference frequency signal source of various electronic devices and apparatus such as communication apparatus and electronic watches.

However, when used practically, the ATcut thickness shear quartz crystal oscillator encounters various problems. To reduce the size of the oscillator without degrading its frequencytemperature characteristic so that the oscillator may be placed in a small casWg of, for example, an electronic watch, the following problem will arise.

A known thickness shear quartz crystal oscillator is made of a quartz crystal plate which has a rectangular cross section and which extends in the direction of its X axis. The oscillator vibrates in a direction which is parallel to the X axis. To make the oscillator small, the crystal plate is cut at an angle of 341451 to 3520' (hereinafter called -- -cutangle") and is provided with an inclination angle of 21 to 16'. The cut angle and the 95 inclination angle will be defined as follows.

Suppose the X-Z plane defined by the X and Z axes of the crystal plate is rotated about the X axis and that Y' and Z' axes are imagined which incline at the same angle to the Y and Z axes, respectively. Then, the "cut angle- is the angle at which X-Z' plane defined by the X axis and the imaginary Z' axis inclines to the X-Z plane. And the '1nclination angle" is the angle at which the side faces of the crystal plate incline when one of the major surfaces of the crystal plate which are parallel to the X-Z' plane is displaced in the direction of the imaginary Z' axis.

If cut at said cut angle and provided with said inclination angle, the crystal plate has its width reduced or it becomes shorter in the direction of the Z' axis, without deteriorating its own frequency-temperature characteristic which is represented by a three- dimensional curve with an inflection point at about the room temperature. The above-mentioned method of shaping a crystal plate, however, fails to make the plate shorter in the direction of the axis X. That is, the method cannot reduce the length of the crystal plate, for the following reason.

As disclosed in "30th Annual Symposium on Frequency Control-1 97W' pages 196-201, an AT-cut quartz crystal oscillator having a cut angle of 35130', a length a along the X axis and a thickness b along the Y axis will have its 1,25 frequency-temperature characteristic changed if the length a is reduced a little so that the ratio of a to b decreases from 2.935 to 2.745. More specifically, the inflection point will appear at a temperature of 601C to 801C. That is, if the length of an AT-cut quartz oscillator is reduced, the inflection point will appear at a temperature far higher than the room temperature, and the threedimensional curve showing the characteristic will become almost twodimensional in the vicinity of the room temperature. If this happens, the quartz crystal oscillator cannot be used practically.

An object of this invention is to provide a thickness shear quartz crystal oscillator which can be made small and light and whose length can be reduced without deteriorating the electric characteristics.

To accomplish the object, a thickness shear quartz crystal oscillator according to this invention comprises a quartz crystal plate having two major surfaces which extend in the direction of X axis of the crystal plate, are 5mm to 1 Omm long and are parallel to X-Z' plane defined by the X axis and an imaginary Z' axis inclining to Z axis of the crystal at 35108'to 35116', one of the major surfaces being displaced in the direction of the Z' axis thereby to cause the side faces of the crystal p-late to incline at an angle of 41 to 61.

Comprised of such a quartz crystal plate, the thickness shear quartz crystal oscillator exhibits a frequency- temperature characteristic which is represented by a three-dimensional curve with an inflection point at about the room temperature. The oscillator is therefore stable against temperature variation. Further it can be made small and light because its length can be reduced without deteriorating its electric characteristics. Still further, it remains resistant to impact even if a pair of electrodes are led out from one of its ends.

If led out in this way, the electrodes can be connected to lead wires of an external device, much easier than if one of them is led out from the other end of the oscillator. This helps enhance the efficiency of manufacture, particularly when the oscillators are manufactured in large quantities.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagram illustrating the cut angle, inclination angle and length of a thickness quartz crystal oscillator according to this invention; Fig. 2 is a graph showing the relationship between the lengths of oscillators of this invention and the temperature at which the inflection point appears, when the oscillators have different inclination angles and are excited with fundamental waves having a resonance frequency of 4 MHz; Fig. 3 is a graph showing the relationship between the resonance frequency and the temperature at which the inflection point appears, when the oscillators are 5mm long and have different inclination angles; Fig. 4 is a graph showing the relationship between the ambient temperature and-the rate of frequency change of the oscillators, with respect to oscillators have different cut angles; Fig. 5 is a perspective view of a thickness shear 2 GB 2 043 996 A 2 quartz crystal oscillator according to this invention; Fig. 6 shows the oscillator of Fig. 5 unfolded, illustrating how electrodes are formed on the major surfaces of the oscillator by vapor deposition; Fig. 7 is a front view of the oscillator of Fig. 5, which is provided with electrodes vapor deposited; Fig. 8 is a side view of the oscillator of Fig. 5; 75 and Fig. 9 is a perspective view of the oscillator shown in Figs. 6 to 8, which is secured to a base.

Now referring to the accompanying drawings, embodiments of the invention will be described.

A thickness shear quartz crystal oscillator of this invention comprises such a quartz crystal plate as shown in Fig. 1. The crystal plate / has two parallel major surfaces 2 which extend in the direction of X axis of the crysta I plate / X-Z plane defined by.the X and Z axes of the crysial plate / is rotated about the X axis by 35108' to 35116', thus providing imaginary Y' and Z' axes which incline to the Y and Z axes of the plate respectively, at the same angle of 35'08'to 90 35116'. As a result, the major surfaces 2 are positioned parallel to X-Z' plane defined by the X and Z' axes. The upper major surface 2 of the crystal plate i is displaced in the direction of the Z' axis, thereby to cause the side faces of the plate /to incline at an angle of 41 to 60 (hereinafter called "inclination angle").

A number of thickness shear quartz crystal oscillators were made. They comprised crystal.

plates having the same thickness, the same width 100 of 1.4mm, the same cut angle of 351 10', different inclination angles of 2 0, 50 and 100 and different lengths ranging from 3mm to 15mm.

Fundamental waves having a resonance frequency of 4 MHz were applied to the oscillators.

(Fundamental waves having a resonance frequency other than 4 MHz may of course be applied to the oscillators). Then, the oscillators exhibited frequency-temperature characteristics which represented by three-dimensional curves with inflection points. The oscillators which were 1 Omm or more long showed such frequency temperature characteristics with inflection points appearing at about the room temperature, no matter whether their inclination angles were 20, or 100. The oscillators which were less than 1 Omm long and had inclination angles 21 and 101 exhibited frequency-temperature characteristics with inflection points appearing at temperatures far higher than the room temperature. These oscillators could not therefore be used practically.

By contrast, the oscillators which were less than 10mm long and had an inclination angle of 51 exhibited frequency-temperature characteristics with inflection points appearing at relatively low temperature, and these oscillators could be used practically. The results of this experiment shows, as illustrated in Fig. 2, that a thickness shear quartz crystal oscillator can be used practically if it is 5mm to 1 Omm long and has an inclination 130 angle of 4' to 61, because the inflection point appears at about the room temperature.

Further, a number of thickness shear quartz crystal oscillators were made. They comprised quartz crystal plates having the same thickness, the same width of 1.4mm, the same length of 5mm and the same cut angle of 35110'. Fundamental waves having different resonance frequencies were applied to these oscillators. Then, they exhibited frequency-temperature characteristics with inflection points appearing at such temperatures as illustrated in Fig. 3. As Fig. 3 shows, the temperature at which an inflection point appears depends on the inclination angle of the crystal plate. More specifically, when fundamental waves having a resonance frequency of 15 MHz or more were applied to the oscillators which had inclination angles of 21, 50 and 100, the inflection points appeared at about the room temperature. When fundamental waves having a resonance frequency of less than 15 MHz were applied to the oscillators which had an inclination angle of 2 0 or 100, the inflection points appeared at so high temperatures that the oscillators could not be used practically. The results of the experiment show that a thickness shear quartz crystal oscillator which has an inclination angle of 5' or about 51 and is 5mrn to 1 Omm long exhibits a frequency-temperature characteristic with an inflection point appearing at about the room temperature.

As generally known, the frequency-temperature characteristic of an AT-cut thickness shear quartz crystal oscillator depends on the cut angle of its quartz crystal plate. A number of thickness shear quartz crystal oscillators were made. The oscillators comprised quartz crystal plates having the same thickness, the same width of 1.4mm, different lengths of 5mm to 1 Omm and different inclination angles of 35105', 35108', 35112', 3W1 6' and 35120'. The output frequencies changed at different rates according to the ambient temperature as illustrated in Fig. 4. As Fig. 4 shows, the frequency changed at the rate of -30 ppm to +30 ppm at -1 01C to +601C as far as the oscillators having a cut angle of 350081 to 35116' are concerned. In other words, the oscillators having a cut angle within this range could be used practically. On the other hand, the frequency changed more abruptly -1 OOC to +60'C as far as the oscillators having a cut angle outside this range are concerned. In other words, the oscillators having a cut angle of less than 35'08' or larger than 35116' could not be used practically.

In the oscillators which were made and used in the above-mentioned experiments, the quartz crystal plates had the same width of 1.4mm. The width the plates is not limited to 1.4mm, of course.

Accordingly, a thickness shear quartz crystal oscillator of this invention comprises a quartz crystal plate which has a length of 5mm to 1 Orrim along the X axis, a cut angle of 35108'to 350161 and an inclination angle of 41 to 61. Provided with 3 GB 2 043 996 A 3 such quartz crystal plate, the oscillator exhibits a frequency- temperature characteristic which is represented by a three-dimensional curve with an inflection point appearing at about the room temperature. The length of the crystal plate can be reduced without deteriorating the electric 50 characteristics. Thus, the oscillator can be made small and placed in a small case of an electronic.

wristwatch.

As mentioned above, the electric characteristics of the thickness shear quartz 55 crystal oscillator according to this invention are not deteriorated even if the length of the quartz crystal plate is reduced. The impact-resistance of the oscillator will not be degraded if a pair of electrodes are led out from one of the ends of the crystal plate.

Now referring to Figs. 5 to 9, an embodiment of this invention will be described, in which a pair of electrodes are led out from one of the ends of a quartz crystal plate and are secured to a base.

Fig. 5 shows a thickness shear quartz crystal oscillator comprising a crystal piece 3 which has a length, a cut angle and an inclination angleall within the above-mentioned ranges. The quartz crystal piece 3 has a curving surface. This piece 3 can be obtained by beveling the ends of a quartz crystal plate having a cut angle of 35008' to 350 16', by placing the plate in a barrel together with an abrasive and by rotating the barrel at a high speed. An exciting electrode 5 is formed on one of the major surfaces of the piece 3 by vapor deposition, and a lead electrode 6 is formed on the same major surface also by va por-cle position.

Fig. 6 shows the oscillator of Fig. 5 unfolded.

Figs. 7 and 8 are the front and side views of the oscillator of Fig. 5, respectively. As Figs. 6, 7 and 8 80 show, on the other major surface of the crystal piece 3 there are formed another exciting electrode 7 and another lead electrode 8, both by vapor-deposition. These electrodes 5, 6, 7 and 8 can be easily vapor-deposited on the major Surfaces of the piece 3. Further, the electrodes 5 and 6 are mutually connected merely by forming them so as to overlap them one upon the other, thus without using a lead wire or a electrically conductive adhesive. The electrodes 7 and 8 are mutually connected in the same way. The lead electrodes 6 and 8 can be easily connected to external lead wires if they are so formed as to bend around one end of the oscillator 3, thus enhancing the efficiency of manufacture.

Fig. 9 shows the thickness shear quartz crystal oscillator standing upright on a base 9. The lower end of the crystal piece 3 is bonded to the base 9 with an adhesive agent 10, and the lead electrodes 6 and 8 are connected to external terminals 12 through lead wires 11. If the piece 3 is supported on such a base, it is sufficiently resistive against impact because its length is reduced.

Claims

1. A thickness shear quartz crystal oscillator comprising a quartz crystal plate having two major surfaces extending in the direction of X axis of the crystal plate, being 5mm to 1 Omm long and being parallel to X-Z' plane defined by the X axis and an imaginary Z' axis inclined to Z axis of the crystal plate at 35108' to 35016', one of said major surfaces being displaced in the direction of V axis thereby to cause the side faces of the crystal plate -to incline at an angle of 41 to 61.

2. The thickness shear quartz crystal oscillator according to claim 1, which is excited with a fundamental harmonic frequency of 15 MHz or more so as to exhibit a frequency-temperature characteristic with an inflection point which appears at about the room temperature.

3. The thickness shear quartz crystal oscillator according to claim 1, wherein said major surfaces have such a length that the oscillator may be secured to a base in such a manner that a pair of lead electrodes are led out from one end of the oscillator and connected to external lead wires.

4. Thickness shear quartz crystal oscillator, substantially as hereinbefore described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies maybe obtained.